June 24 (Reuters) - Major Canadian oil pipelines that move
almost 1 million barrels per day (bpd) of Alberta oil sands
crude remained shut on Monday, after a spill on a smaller line
was discovered on the weekend, operator Enbridge Inc
said.

Enbridge, Canada's largest pipeline company, said on
Saturday that 750 barrels of synthetic oil had spilled from the
17-km (11-mile) Line 37, which serves CNOOC Ltd's Long
Lake oil sands project in northern Alberta. The rupture was
spotted about 70 km (43 miles) southeast of the city of Fort
McMurray.

The spill, which may have been caused by heavy flooding that
has paralyzed the Alberta city of Calgary, headquarters of
Canada's oil and gas industry, forced Enbridge to shut two much
larger lines as a precaution, threatening a serious disruption
in the flow of oil sands crude.

The 345,000 bpd Athabasca pipeline, which carries dilbit
blended crude to the Hardisty terminal in Alberta, and the
Waupisoo line, which can carry up to 600,000 bpd depending on
crude viscosity, to Edmonton, Alberta, were both shut.

Those are two of the biggest lines that carry crude from the
northern production centers around Fort McMurray to the storage
and pipeline hub in Hardisty, Alberta, connecting to Enbridge's
main export pipeline that runs into the United States.

Enbridge returned a section of the Athabasca pipeline
between Cheecham, south of Fort McMurray, and Hardisty late
Sunday.

"The line segment north of Cheecham remains shut down until
Enbridge can ensure its safe restart," the company said in a
statement Monday.

"The Waupisoo pipeline from Cheecham to Edmonton is
undergoing an assessment today and may be cleared for restart as
early as tomorrow," it added.

The shutdowns have forced Suncor Energy to
temporarily scale down production from its Fort McMurray
operations.

Traders said the line closure had helped support U.S. crude
oil futures, which rose $1.49 to $95.18 a barrel,
relative to Brent crude, which gained only 25 cents to $101.16 a
barrel on Monday.

The Brent/WTI spread narrowed as low as $5.91 during the
trading day, the lowest level since Nov. 2011. Cash crude
differentials in the United States were little impacted by the
disruption, however, traders said.

On Monday, Enbridge said around 75 workers were at the site
of the pipeline leak, which occurred in a remote area accessible
by helicopter and all-terrain vehicles.

The leak was contained within Line 37's right of way and
there have been no reports of harm to wildlife.

The spill threatens to fan growing criticism of the safety
of the North American pipeline network and of expanding
production of oil sands crude. A string of incidents in recent
years has drawn attention to oil shipments.

Separately, Spectra Energy said it had restarted its
Express-Platte pipeline system on Saturday after shutting the
line as a precautionary measure on Friday after heavy flooding
caused some communication issues.

The 280,000 bpd Express line carries crude from Hardisty to
Casper, Wyoming, while the 164,000 bpd Platte line continues to
Wood River, Illinois.